Studies were directed toward defining the role of disorders of immunoregulatory cell interactions in the pathogenesis of immune dysfunctions. Leukemias of prosuppressors, suppressor effector and helper T cells have been identified. Excessive numbers of suppressor T cells have been demonstrated in association with agammaglobulinemia, selective IgA deficiency, suppressor leukemias, infectious mnonucleosis, and post transplantation immunodeficiency states. Antigen nonspecific suppressor factors that inhibit B cell immunoglobulin synthesis have identified in the supernatants of cultured human T cell lines and T-T cell hybridomas. The structure and function of the IL-2 receptor has been elucidated using a monoclonal antibody to this receptor. Recombinant DNA technology has been applied to the study of the arrangement and rearrangement of immunoglobulin genes in lymphocytic leukemias. Unexpectedly the kappa gene was deleted or aberently rearranged in all lambda expressing B cells. A hierarchy of gene rearrangements was suggested with a rearrangement of heavy chain genes preceeding light chain genes and kappa gene rearrangements or deletions preceeding lambda.